(1) Field of the Invention
The invention is related to an aircraft with a fuselage that defines at least one drive system accommodating region, the drive system accommodating region accommodating at least one engine that generates a hot air flow in operation of the aircraft, wherein at least one hot air exhaust is provided for exhausting the generated hot air flow, said aircraft comprising the features of claim 1. The invention is further related to a method of operating a hot air exhaust of an aircraft with a fuselage, the hot air exhaust being adapted for exhausting a hot air flow that is generated by at least one engine of the aircraft in operation, said method comprising the steps of claim 12.
(2) Description of Related Art
A fuselage of an aircraft, and in particular of a rotary-wing aircraft, generally defines an interior region and a drive system accommodating region that is arranged inside the fuselage. The interior region usually comprises at least a cockpit and may further comprise a cabin for passengers and/or cargo. The drive system accommodating region usually accommodates one or more engines that are adapted for driving the aircraft, e.g. by providing power to an associated power distribution unit, such as a gearbox, which then provides this power to a suitable propelling unit, such as e.g. a propeller, rotor or other.
Typically, the one or more engines are embodied as air breathing propulsion engines, such as diesel engines, gas engines, gas turbines and so on, which combust a fuel/air mix for power generation. In operation, all such air breathing propulsion engines need fresh air, ideally cold air, which is mixed with fuel so that these engines perform sufficiently and satisfactorily.
However, all such air breathing propulsion engines will not only generate power in operation, but also heat that must be dissipated from the engines for preventing an overheating thereof, which is crucial for the entire aircraft performance, safety and reliability. Generally, such heat is transformed into hot air flows that are dissipated from the engines and exhausted from the rotary-wing aircrafts via suitable hot air exhausts provided at the fuselages.
Usually, the hot air exhausts of rotary-wing aircrafts are implemented by means of straight or mostly straight exhaust ducts. These exhaust ducts guide generated hot air flows from the engines through associated engine cowlings. The main reason for making these exhaust ducts as straight as possible is an aerodynamic friction loss that would occur if the generated hot air flows would not be exhausted at least approximately coaxial to a longitudinal axis of the rotary-wing aircraft, but with a predefined deflection angle relative thereto.
The straight or mostly straight shaping of the exhaust ducts and their conventional arrangement at the fuselages leads to beams of generated hot air flows which are usually guided quite close to the rotary-wing aircraft, leading to local heating-up of the aircraft's airframe structure, especially in an intermediate structure and/or corresponding tail boom areas close to respective exhaust duct outlets. However, such a local heating-up may damage or even destroy the intermediate structure and/or corresponding tail boom areas, if they are excessively heated up above an underlying operational limit of structural materials used. Therefore, counter measures must be taken in order to avoid such an excessive heating-up, in particular of load-carrying structural parts of the rotary-wing aircraft.
One conventional counter measure for protecting load-carrying structural parts of rotary-wing aircrafts against excessive heating-up consists in providing heat-insulation/shielding panels mounted on top of the load-carrying structural parts. Such panels are usually spaced apart from the corresponding load-carrying structural parts so that a gap is provided that allows air ventilation between the panels and the corresponding load-carrying structural parts. Furthermore, the panels can be painted with heat-resistant, mate black or anthracite top coats. However, such heat-insulation/shielding panels are usually adding extra weight onto the aircraft's airframe structure. Also, they create additional aerodynamic drag and disturb respective exterior aspects/designs of rotary-wing aircrafts.
Another option for protecting load-carrying structural parts of rotary-wing aircrafts against excessive heating-up by means of beams of exhausted generated hot air flows consists in providing longer and/or bended exhaust ducts. However, longer and/or bended exhaust ducts create aerodynamic friction within the exhaust ducts and are, therefore, reducing available engine power and decreasing fuel efficiency.
Still alternatively, the load-carrying structural parts can be implemented with structural materials that are able to cope with higher service temperatures in order to avoid provision of heat-insulation/shielding panels and/or longer and/or bended exhaust ducts. However, materials that are able to cope with such higher service temperatures are usually expensive and labor-intensive during manufacturing. Therefore, this alternative is generally avoided due to massive cost drawbacks.
Still alternatively, exhaust ducts can be cooled by suitable cooling means. By way of example, the documents EP 1 887 208 A2 and EP 1 817 490 A1 describe cooled exhaust ducts. However, such cooled exhaust ducts are generally expensive and complicated to manufacture.
The documents U.S. Pat. Nos. 4,679,732 A, 4,248,041 A, 4,132,089 A, 3,837,578 A, 3,525,475 A, 3,451,624 A, 3,400,540 A, 3,441,220 A, 3,355,889 A, 3,180,087 A, 3,067,579 A and 2,933,891 A describe vectorable, i.e. at least partly rotatable exhaust ducts, where at least one first exhaust section is mounted in a rotatable manner to at least one second exhaust section. However, these vectorable exhaust ducts define jet pipes that are used for expelling thrust gases of aircraft jet engines for generating propulsive jets.